In the field of the manufacture and treatment of moulded parts, it is customary to specifically manufacture moulded parts having the desired material properties. In the automotive industry for example, parts such as transverse links, B-columns or bumpers for motor vehicles are hardened by being heated completely and subsequently quenched. For hardening, this can be followed by a tempering process. However, for some automotive engineering applications it is an advantage when moulded parts have different material properties in different portions. It could, for example, be required that a part has high strength in one portion but should in comparison have higher ductility in another portion.
In order to realize moulded parts which can satisfy various strains and stresses in different portions, parts with differing properties can, for example, be joined. Further, parts can be strengthened by additional sheet metal. Another option is the soft annealing of the appropriate portions of previously completely hardened moulded parts in order to achieve portions with higher ductility. This, however, leads to changes in the form of the part which are not tolerable.
Additionally, there is the option to treat moulded parts during manufacture so that portions with different material properties are generated. In this case, portions with different structures develop and various state of the art technological processes and facilities are known for the manufacture of moulded parts with at least two structural areas. For example, the use of induction current to heat parts is known. In this case, however, high costs and non-uniform heating are to be expected.
Further, European patent application EP 1 426 454 A1 discloses a process to manufacture a moulded part with at least two structural portions of differing ductility and a continuous furnace to carry out the process. In this case, a semifinished product in the form of a blank or pre-formed part which is to be heated is transported through a continuous furnace comprising two zones arranged side by side in which different temperature levels can be adjusted. The part in the furnace is thus heated to two different temperatures and subsequently subjected to a hot forming process and/or a hardening process. The portion of the part which is subjected to higher heat thereby develops a more ductile structure while the portion subjected to lower heat develops a strong or high-strength structure.
The German utility model DE 200 14 361 U1 describes a process to manufacture a B-column with differing structural areas by which the B-column is heated in a furnace and thus austenitized and subsequently hardened in a cooled tool. When heating in a furnace, large portions of the used blank and/or semifinished product are insulated against the effects of temperature so that no martensitic material structure with high strengths can develop in the shielded portions. However, this process is unsafe because in the case of operational malfunction, heat can penetrate the shielded portions and thus also heat these portions to hardening temperature.
In particular, the known processes are particularly unsuitable for mass operation with a cycle time of approximately 15 seconds and for process reliability as is required for the manufacture of automotive vehicles because they cannot permanently ensure the specified hardening profile in the part.